Xenopus connexin38 forms hemi-gap-junctional channels in the nonjunctional plasma membrane of Xenopus oocytes

A nonselective cation current activated by depolarization (Ic) is present in the nonjunctional membrane of Xenopus oocytes. This current shares a number of properties with hemi-gap-junctional currents induced by exogenous gap-junctional proteins in oocytes and with a nonjunctional current seen in teleost retinal horizontal cells including nonselective permeability to small cations, block by external divalent cations, and slow activation kinetics. Here we study the effects of depleting or overexpressing Cx38 on Ic. Antisense depletion of Cx38 caused a marked reduction in Ic and blocked endogenous gap-junctional coupling in oocyte pairs. Conversely, expression of cloned Cx38 in oocytes increased the amplitude of Ic and enhanced gap-junctional coupling. Furthermore, there appeared to be a close correlation between the temperature sensitivity of Ic and the temperature sensitivity of assembly of endogenous gap-junctional channels in oocyte pairs. These results suggest that Xenopus connexin38 is involved in the generation of Ic